4-5 inches in front of the oil sending unit pressure gauge sender of place for a mechanical gauge is a threaded fitting with a plug. Mine is an Allen Head. It is directly inline with the oil galley on the side of the block very close to the fuel pump. I can just barely feel a threaded hole on the front face of the block around the corner from it..... Any know what it is? Water...Oil...nothing...

56 Vic, B'Ville 200 MPH Club Member, So Cal.